This invention relates to hydroforming apparatus and more particularly to devices for locating a tubular part for engagement by the seal units in the apparatus while also locating the part between the dies of the apparatus.
In the apparatus for hydroforming a tubular part, there is typically a lower die and an upper die that are pressed together to form a die cavity that extends about the part. Wherein the cavity has the shape to which the part is required to be formed and extends to opposite end portions of the dies and wherein the part has ends that extend beyond the ends of the dies for engagement by seal units that deliver hydraulic fluid under pressure to the interior of the part and later provide for exhausting this fluid. To reduce cycle time as well as prevent against possible bending or collapse of the part prior, to and/or during die closure, the part can be prefilled with the hydraulic fluid at a relatively low pressure and this requires that the seal units sealingly engagement with the end portions of the part prior to the dies closing on the part. And for such seal unit engagement with the part prior to die closure, it is important that the end portions of the part be accurately aligned with the seal units to effect their sealed engagement. As otherwise, proper sealing may not be obtained and the part and/or the seal units may be damaged.
The seal units may also be used to center the part lengthwise with respect to the dies prior to die closure through their engagement with the ends of the part. In that case, it is important that when the seal units are caused to engage with the ends of the part for such centering operation they do so in an efficient and reliable manner. Moreover, because the end portions of the part project from the dies for engagement with the seal units, there is the possibility that any projecting end portion of the part not captured by the seal units may burst during the hydroforming of the part and result in having to scrap the part.
An example of hydroforming apparatus that does provide for accurate alignment of projecting end portions of a round tubular part with the seal units is disclosed in U.S. Pat. No. 5,321,964 assigned to the assignee of this invention. As disclosed therein, each of the seal units is provided with a locator member and a backup member. The backup members are fixed with respect to the upper die and the locator members and their associated seal unit are mounted on separate elevators that are supported by springs with respect to the lower die. With the seal units retracted, the tubular part is loaded such as by a robot and at what will be its projecting end portions onto the locator members which locate the end portions in alignment with the respective seal units while the seal units and locator members are located and held by their respective elevator at an elevated position with respect to the lower die. The seal units are then extended to sealingly engage the respective end portions of the part while centering the part lengthwise with respect to the dies. The upper die is then lowered onto and pressed against the lower die to form the die cavity about the part. As the upper die is lowered to form the die cavity, this upper die movement also causes capture of the projecting end portions of the part between the respective locator and backup members as the dies are pressed together. This upper die movement also causes lowering of the elevators and the seal units and thereby the part engaged by the seal units whereby an inward region of the end portions of the part are ultimately received in alignment with terminal end portions of the die cavity as the dies are pressed together about the part.
While such apparatus has proven to provide satisfactory alignment of the part with the seal units, it has been found that because the end portions of the part are not fully radially restrained by the locator members of the respective seal units during the engagement of the seal units with the part prior to die closure, the part may bounce or be jostled and as a result interfere with the centering of the part with respect to the dies by the seal units and possibly result in damage to the part and/or the seal units.
One successful way of solving such problems is disclosed in co-pending U.S. patent application Ser. No. 10/278,428 filed Oct. 23, 2002 entitled xe2x80x9cTUBULAR PART LOCATOR FOR HYDROFORMING APPARATUSxe2x80x9d and assigned to the assignee of this invention. In this apparatus, each seal unit is provided with a tubular part locator comprising a locator member directly associated with the seal unit in a fixed relationship, a backup member rigidly fastened to the upper die and a pair of clamping arms that are pivotally mounted on the locator member and are operated by separate pneumatic cylinders. And the seal units and their associated locator member and clamping arms are all mounted on separated elevators at the opposite ends of the dies.
The locator members have a concave surface and adjoining guide surfaces wherein the concave surface is of limited extent and conforms to the outer surface of the part and has a centerline coincident with that of the seal unit. And the guide surfaces on the respective locator members are adapted to guide the respective end portions of the part onto the concave surface of the locator members and thereby into alignment with the respective seal units.
The clamping arms also have a concave surface conforming to the outer surface of the part but of substantially less extent than the concave surface of the locator member and are adapted on pivotal movement by their pneumatic cylinder to clamping positions to clamp the end portion of the part on the concave surface of the locator member to thereby prevent bouncing or jostling of the part while the seal unit is then brought into sealing engagement with the end portion of the part. The backup member also has a concave surface of limited extent conforming to the outer surface of the part and is adapted to move with the upper die to a backup position as the upper dies closes on the part where its concave surface then helps clamp the end portion of the part on the concave surface of the locator member.
The backup member when in its backup-clamping position is also adapted to hold the clamping arms in their clamping position during hydroforming of the part to thereby relieve the pneumatic cylinders of having to resist the hydroforming force acting in the end portion of the part outward on the pivot arms. And the combined concave surfaces of the locator member, clamping arms and backup member by completely encircling the end portion of the part between the dies and the respective seal unit act to prevent bursting of the end portion of the part during the hydroforming operation.
While the above described forms of hydroforming apparatus have proven successful, there remains a desire to both simplify and compact the apparatus while maintaining the tubular part locators with accurate locating ability and sufficient clamping ability. Moreover, there remains a desire to shorten the length of the tubular stock required to produce the part in the hydroforming operation to thereby save material and reduce cost.
To these ends and in accordance with the present invention, the seal units that are located at opposite end faces of the dies remain supported on separate elevators that are adapted to locate the seal carriers of the respective seal units in alignment and to elevate the seal units to a first position for initial engagement of the seal carriers with the respective end portions of the tubular part when the dies are open. And the tubular part locators are adapted to locate and firmly hold the end portions of the tubular part for engagement by the seal carriers in a manner similar to previous practice but instead of being mounted in a fixed relationship with the respective seal units are now made retractable with the latter operation being accomplished by also mounting them on separate elevators. Wherein the retractable part locators including their elevators are made very compact with the part locator elevators being provided by compact slide mechanisms that are operated by pneumatic or hydraulically operated actuators and being located to between the respective seal unit elevators and the end faces of the dies.
The part locator elevators are adapted to cooperatively elevate the part locators to positions where they receive and locate and hold the end portions of the tubular part in alignment with the respective seal carriers of the seal units when the seal units are in their aforementioned first position and the dies are open. And also while the seal carriers are caused to then advance and initially be received on the respective end portions of the tubular part. The part locators are adapted to then release the end portions of the tubular part after this initial seal carrier advancement and the part locator elevators are adapted to then lower the part locators to positions out of the way of the respective seal carriers so as to permit the seal carriers to then be further advanced on the respective end portions of the tubular part to points closely adjacent a plane containing the respective end faces of the dies. The seal units are effectively sealingly engaged with ends of the tubular part during the latter and final advancement of their seal carrier and the part can then be prefilled prior to containment of the part in the dies to prevent possible distortion of the part during die closure. The seal unit elevators are adapted to then lower the respective the seal units together with the tubular part to the aforementioned second position where the dies close on the prefilled tubular part.
As a result, the end portions of the tubular part that project from the ends of the dies are fully received in the seal carriers of the seal units for the hydroforming operation that then takes place and are thereby fully contained by the seal units and very effectively prevented from bursting by the high hydroforming pressures that are used. Furthermore, this is accomplished with a very compact hydroforming apparatus arrangement wherein the retractable part locators are made compact as well as their elevators, which are separate from the seal unit elevators that thereby only need to support the seal units. Moreover, the end portions of the part that project from the dies only need to be long enough to provide for sealed engagement with the seal units thereby minimizing the length of tube stock needed in the processing of the hydroformed part.
These and other aspects of the present invention including the entire functional capability of the retractable part locators will become more apparent from the accompanying drawings and following detailed description of exemplary embodiments of the invention.